1. Field of the Invention
This invention relates to film winding devices with means for preventing the corner of a film leader from engaging overlapping perforations of the film after the film has turned around the spool one or more turns.
2. Description of the Prior Art
Conventionally, automatic film winding devices for cameras have generally been made such that the narrow leader of the film is manually placed on the takeup spool and, when the back cover is closed, it is then automatically caught up on the spool with the help of a pressure roller as the film transportation mechanism starts to operate. In this type of winding device, however, because the pressure roller is constructed with large diameter portions in the upper and lower ends thereof by which the film is pressed against the spool, there is a tendency for it to act on only one of the edges of the film, or on the lower edge (under the normal loading condition) as far as the film leader is concerned. Therefore, the use of a peripheral speed on the spool faster than on the sprocket as is well known in the art of cameras in combination with such means as described above leads to a pull on the film only in the lower edge so that the peripheral speed of the lower edge is greater than that of the upper edge and the film leader is helically convoluted on the spool as illustrated by dot-and-dash lines in FIG. 1.
Upon occurrence of this phenomenon, the lower corner 7a' of the film leader 7a after having made one turn around the spool 1 bites into the following perforations of the film as illustrated in FIG. 2 with the formation of a closed round loop of far larger diameter than that of the takeup spool 1 to thereby develop a gap, g, between the film and the spool as illustrated in FIG. 3. Thus, when more of the film is fed, the outer periphery of the convoluted film contacts with the wall of the takeup spool chamber and as a result no more film can be wound up.
Also, as illustrated in FIG. 4, the winding means may be otherwise constructed by providing teeth 2 on the periphery of the lower flank of the spool 1 to assist in making sure the film leader is engaged by the teeth 2 engaging the perforations of the film (as, for example, in the Konica PS-1 and Fujica Auto 5 cameras). In this case, as the film is pulled by one or two of the teeth 2, a front portion of the film leader ahead of the perforations which engages the tooth 2 floats up from the spool 1 as illustrated in FIG. 4 and tends to move away from the spool 1. Along with this, because the film leader 7a has perforations only in the lower vicinity, the lower edge of film is driven to move at a faster speed than the peripheral speed of the upper edge. Even in this example, therefore, as in the above, the film leader is caused to convolute helically on the spool as illustrated in FIG. 1. Also in the case of this example, there is a high probability that the lower corner 7a' of the narrow film leader 7a after having turned around the spool will engage in the following perforations 8.
Attempts have been made to eliminate the above-described drawbacks by providing a frictional member on the outer periphery of the spool against which the film is pressed by a roller so that as the film leader is impelled laterally to move to the outside, the film leader corner can shift in position so as not to engage the perforations of the following area of film (as, for example, employed in the Konica FS-1 camera). Cameras of this type use a spool such as that disclosed in U.S. Pat. No. 4,274,726, wherein a larger diameter portion is provided at the end of the spool on which the film is directly wound in contact therewith. Since spools of this type involve differences in the diameter thereof, by which diameter differences the film leader is made to move laterally, the spool itself is complicated in structure, and the frictional member and the roller too must be provided for the respective portions of the spool which have different outer diameters, thus giving rise to disadvantages in that difficult production techniques are required and that the production cost is also considerably increased.